There is strong evidence showing an overall essential role of catecholamines in the regulation of gonadotropin release by the hypothalmus. Accordingly, there are three possible sites of action for the amines, namely, the median eminence, the portal system and the pituitary. Neither of the three sites is exclusive of the others. We have recently demonstrated a possible direct action of dopamine on LHRH-induced LH release in estrous rabbits. Therefore, we propose to investigate the direct hypophysial action of dopamine and norepinephrine on LH, FSH, and prolactin release in the rabbit. Taking the advantage that the rabbit has a separate arterial supply to the pituitary independent of the hypophysial portal supply and that the estrous rabbit responds to an ovulatory stimulus by cupric acetate injection, we plan to develop an in vivo isolated, referring to the isolation from hypothalamic influences, pituitary experimental model in order to study the direct action of catecholamines on the pituitary. First, catecholamine release into the pituitary portal blood by a cupric acetate stimulus will be determined by stalk cannulation and a sensitive electrochemical catecholamine assay. Second, based on the portal catecholamine and LHRH release patterns, the pituitary responses to catecholamines on gonadotropin release will be determined in a superfused pituitary under total in vitro conditions. Our overall objective is to determine whether the catecholmaines directly affect pituitary LH, FSH and prolactin release. Specific aims are: a. Establishment of an in vivo pituitary model; b. Establishment of an in vitro pituitary model; c. Determination of catecholamine release in the pituitary portal vessels during an induced ovulatory reflex; and d. Investigate qualitative and quantitative differences in the effect of catecholamine in the in vitro and the in vivo pituitary models. Elucidation of the major site of action of hypothalamic catecholamines shall enhance our understanding of the mechanism of action of catechols in the regulation of reproductive function. The in vivo pituitary model shall be a powerful tool for the future study of hypothalamic factors and their interactions.